Technical Field
The present invention relates to the field of biological technology, particularly to a method for determining nucleic acid composition in a nucleic acid mixture, and more specifically to a method for determining the content of a first nucleic acid in a total nucleic acid mixture comprising the first nucleic acid and a second nucleic acid.
Related Art
Prenatal diagnosis is one of the most efficient ways to reduce congenital anomalies by diagnosing congenital defects or genetic diseases in a fetus before birth using various detection tools, for example, imaging, biochemical, cytogenetic, and molecular biological technologies.
Since 1997, research has shown that cell-free fetal DNA is present in the peripheral blood of a pregnant woman, and this finding generates a new opportunity for noninvasive fetal screening.
In the existing method for detecting fetal chromosomal aneuploidy by sequence analysis of the maternal plasma, the total free DNA in the maternal plasma is generally sequenced, without making a discrimination between the fetal and maternal DNA, and whether the fetus has chromosomal aneuploidy is determined using a significance test. The method has certain advantages in noninvasive screening of trisomies. However, when the fetal DNA concentration is low, a false negative result may potentially be obtained due to a low significance of the chromosomal abnormality.
Therefore, there is a need for an improved method for quantifying the fetal DNA in the maternal plasma.
DNA methylation refers to a chemical modification process in which in the presence of a DNA methyl transferase, a methyl group is added to the C-5 carbon of cytosine, to produce methylcytosine. Such a DNA methylation modification may be individual-, tissue- or cell-specific, such that the DNA from different sources (for example, fetal versus maternal DNA, or tumor versus normal DNA) can be discriminated based on the methylation of a particular gene, allowing the DNA from a source to be quantified.
For detection of cancers at an early stage, the methylation of a particular gene is closely linked to the occurrence and development of cancers, and thus can be used as a potential marker in early diagnosis. For example, colorectal cancer, also referred to as large intestine cancer, involves the proliferation of tumors in the large intestine, the rectum and the appendix. In the western world, it is the third most prevalent cancer, and the second leading cancer-causing death. Generally, it is thought that many large intestine cancers originate from the adenomatous polyp of the large intestine. These mushroom-like tumors are generally benign, but some of them develop into cancers after a period of time. Colon cancer may be effectively treated at an early stage by surgical operation before metastasis, to prolong survival time. Therefore, the detection of colorectal cancer at an early stage is a key factor determining whether a successful and absolute cure can be achieved. A highly specific and sensitive marker is crucial for the diagnosis of colorectal cancers. For example, qualitative and quantitative detection of abnormally high DNA methylation in serum and excrements is a new, highly promising, and non-invasive method for screening for colorectal cancer.